Climate has changed in the past through natural causes, on timescales ranging from hundreds to millions of years.

Past climate change on different timescales

This graph of average long term temperature change shows patterns of warm, cool and cold periods over the past 450,000 years. When the temperature is cooler, lower than 0° C, more of the earth is covered in ice. This is called an Ice Age or glacial. We are currently in a warmer period, known as an interglacial.

The quarternary period is a geological time period of the most recent 2.6 million years (from the present day).

The ‘Ice Ages’ in the Quaternary Period.

The entire

UK climate since Roman times.

Burning fossil

Natural causes of climate change

Asteroid collisions - Large asteroid collisions release dust that can block out the sun and thus lower temperatures. Asteroids can cause large fires when impacting with the ground, the fires release huge amounts of CO2 (a greenhouse gas) that cause a warming effect.

Variations in solar output - Amount of energy from the Sun changes over an 11-year cycle

How natural climate change in the past has affected people and the environment

The impact of a short-term historical event on people and the environmentThe ‘Little Ice Age’:

Colder period in northern Europe starting in 15th century and ending in the 19th.

Crops did not grow well, reducing productivity and meaning less food output.

The winters were very cold and summers short.

Causes of the ‘Little Ice Age’:

Fewer sunspots.

Volcanic ash in atmosphere reducing sunlight.

It was unlikely to be caused by humans because industry wasn’t causing enough pollution at the time.

Evidence of the ‘Little Ice Age’:

Diaries, newspapers and paintings.

Tree rings are thinner during cold years.

Impact of major climatic changes in geological time

The mass extinction of megafauna at the end of the Quaternary Period.

Climate change (along with some influence by humans) meant that megafauna (e.g. mammoths, giant beavers and sabre-toothed tigers) became extinct. Humans couldn’t kill all these creatures, so climate change and a lack of food played a large part in their extinction.Arguments that climate killed megafauna:

They became extinct 5,000 years AFTER humans colonised North America and Europe.

Megafauna couldn’t adapt from the glacial conditions that were replaced by a warmer climate. (They had small ears to reduce heat loss and lots of hair for cold weather).

Australia changed from very cold to warm. This caused lakes and rivers to dry out which killed animals and plants, resulting in death from starvation.